"FaxComEx.FaxDocument.1 Operation failed" when faxing pdf docs

[Guest]

Here's the failure scenario;
Windows service running as a minimal priviledged domain user (not
administrator).
Call to FaxComLibEx ConnectedSubmit from C# hangs code for about 2 minutes
when attempting to fax a pdf in the body of the fax, then throws helpful
"Operation failed" exception.

Success scenario 1;
Same minimal priviledge user account, same service, same scenario except fax
body = .txt file. Every thing works fine.

Success scenario 2;
Domain administrator account running windows service, faxing pdf document in
body of fax. Everything works fine.

So my question is, when the Fax service launches Acrobat as a background
process to handle the doPrint verb, does it require some special account
priviledges?
Does Acrobat try to create folders or temp files to convert the pdf to
faxable tiff files, and if so does the account running the windows service
need special permissions to do this action?

Thanks for you help.